In order to achieve better channel utilization and increase overall performance, multiple transmission and multiple reception antennas (also commonly referred to as multiple input, multiple output (MIMO)) at both base stations (BSs) and mobile stations (MSs) are considered.
Closed loop multiuser multiple input, multiple output (MU-MIMO) technologies recently have attracted attention from both standardization bodies and the telecommunications industry around the world. By jointly taking advantage of multiuser diversity and an inherent space-time diversity of MIMO systems, MU-MIMO may significantly improve system throughput and achieve higher bandwidth efficiency compared to conventional single user MIMO.
The knowledge of channel state information (CSI) is an important factor in wireless communication systems, particularly MU-MIMO systems. Codebook based quantization is a known method for feeding back the channel state information, as taught by Love, et al. (“What is the Value of Limited Feedback for MIMO Channels?” IEEE Communications Magazine, Vol. 42 pp 54-59, October 2004). As is also known, the precision of channel state information plays a key role in achieving the desired gains of Multi-user MIMO systems, per Jindal, (“MIMO Broadcast Channels with Finite Rate Feedback,” IEEE Transactions on Information Theory, Vol. 52, No. 11, pp. 5045-5059, November 2006).
In a MU-MIMO system, if multiple layers per mobile station (MS) are supported, the MU-MIMO precoding may rely on the feedback of channel coefficients, which may imply a very large feedback overhead.